linux-kernel - Re: [PATCH 4/7] mm/hmm: properly handle migration pmd

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Message-ID: <20180828152414.GQ10223@dhcp22.suse.cz>
Date:   Tue, 28 Aug 2018 17:24:14 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Zi Yan <zi.yan@...rutgers.edu>
Cc:     jglisse@...hat.com, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        John Hubbard <jhubbard@...dia.com>
Subject: Re: [PATCH 4/7] mm/hmm: properly handle migration pmd

On Fri 24-08-18 20:05:46, Zi Yan wrote:
[...]
> > +	if (!pmd_present(pmd)) {
> > +		swp_entry_t entry = pmd_to_swp_entry(pmd);
> > +
> > +		if (is_migration_entry(entry)) {
> 
> I think you should check thp_migration_supported() here, since PMD migration is only enabled in x86_64 systems.
> Other architectures should treat PMD migration entries as bad.

How can we have a migration pmd entry when the migration is not
supported?

-- 
Michal Hocko
SUSE Labs